This invention relates to forage harvesters and more particularly to automatic sharpening or grinding apparatus for the knives of the cutterhead.
A number of known forage harvesters fitted with knife sharpening means require a grinding stone to be reciprocated manually back and forth across the rotating cutterhead and this is a very arduous and time-consuming task resulting in operator fatigue and unacceptable downtime of the machine. In other known forage harvesters, such as Great Britain Pat. No. 2,028,191 and U.S. Pat. No. 4,010,576 there are disclosed automatic sharpening mechanisms for forage harvesters in which grinding stones are automatically driven or reciprocated back and forth across the respective cutterheads. In both cases, reciprocation is effected by drive chains which extend around sprocket pairs. As the chains travel around sprockets a coupler is changed from one linear run to another to impart reciprocal retilinear movement to respective carriages.
The disadvantage of these arrangements is that the grinding stones have to be pivoted towards the cutterheads when grinding is required, and then pivoted away on completion of grinding so as to move the stones clear of the cutterheads for normal operation of the forage harvester. Thus the carriage has to be arranged for automatic or manual reciprocatory movement as well as manual pivotal movement and this makes for relatively cumbersome arrangements. Also at least part of the grinding stones remain engageable by the cutterhead knives during the changeover in movement of the carriages from one direction to the opposite direction.
The present invention provides a forage harvester comprising a rotatable cutterhead provided with a plurality of knives the tips of which describe the periphery of a cylinder when the cutterhead is rotated, a grinding mechanism comprising a carriage carrying grinding means and being reciprocable, in the grinding mode, across the cutterhead with the grinding means translating along a line on said cylinder generally parallel to the axis of rotation of the cutterhead, and drive means coupled to the carriage for effecting reciprocatory movement of the latter, the drive means comprising an endless member extending around at least two guide members arranged with their centers on a common line, generally parallel to the axis of rotation of the cutterhead characterized in that the drive means is provided with control means having means for commanding the termination of the grinding mode, and carriage-position-sensing means operable to deenergize the drive means at the end of the grinding mode such as to dispose the carriage in substantially the same position at the end of each grinding mode irrespective of the position thereof at the instant of commanding termination of the grinding mode.
The carriage-position-sensing means may comprise an electric switch which is so disposed as to be operable by the carriage each time the latter returns to the home position, and the command means comprises a timer, the arrangement being such that when the timer runs out, the carriage is not brought to rest until the position sensing switch has been actuated by the carriage next returning to the home position and thus being arrested in that position. Preferably, the drive means may comprise an electric motor controlled by first relay contacts such that when it is deenergized it is connected on both sides to ground, whereby it is brought to rest substantially instanteously so as to ensure that the home position of the carriage is always the same. The home position of the carriage is disposed beyond an associated side wall of a housing for the cutterhead such that, when the carriage is positioned in the home position, the grinding means is spaced from the cylinder described by the tips of the knives when the cutterhead is rotated.